A boat drive of this type is known from U.S. Pat. No. 4,645,463 (H M Arneson) which patent discloses a structure in which the drive body is formed with a ball over which the drive is connected to the drive engine which is mounted inside the boat, and in which said ball is journalled in a ball carrier which is mounted at the stern of the boat, and in which the apparatus comprises two external hydraulic cylinders interconnecting the stern of the boat and a part of the drive for rotating the drive in the horizontal plane for the purpose of turning the boat, and in which there is an additional hydraulic cylinder for making it possible to trim (tilt) the drive by rotating the drive up or down in the vertical direction about the point of rotation of the said ball.
A boat drive of this type having a water surface driving propeller is highly advantageous as compared with the so called Z-drive types, and above all the drive causes less flow losses and less power losses depending on existing angle gear drives and transmission gear sets. Depending on the simple structure of the drive it is also cheaper to manufacture, more effective and apt to less wear and has less sources of error than many other types of boat propulsion drives.
The apparatus known from U.S. Pat. No. 4,645,463 indeed includes the advantages of a drive being a straight, surface water driving propulsion drive, but it is disadvantageous in that the ball and the ball carrier are subjected to strong stresses; in that certain plays may appear in the steering means thereof and in that the hydraulic cylinders for the trimming (tilting) and for the steering operations need to be serviced and maintained, are subjected to wear and are sensitive to ruptures and leakage in the hydraulic conduits, in particular since said parts are located on the exterior side of the boat, behind the stern of the boat. Normally there is also a need for long conduits and/or hoses from the propulsion drive at the outside of the boat to the maneuvre place inside the vessel or boat.